Mystery Class is a global game of hide-and-seek. Follow photoperiod clues to search for ten secret sites around the world. Track sunlight to solve a mystery—and discover the reasons for seasons along the way.

* Please note: Due to budget limitations, our spring 2019 Mystery Class challenge is a replay of a previous year's challenge. We will reveal the locations of the 10 Mystery sites on Monday, April 15th but will not hold a year-end contest.